WorkerExtensionStartupAttribute does not work for F#

# Issue

Types marked with `WorkerExtensionStartupAttribute` are not being called automatically on worker startup when using F#. This is due to this attribute relying on [ExtensionStartupRunnerGenerator](https://github.com/Azure/azure-functions-dotnet-worker/blob/main/sdk/Sdk.Generators/ExtensionStartupRunnerGenerator.cs) (source gen) to function - which does not work for F#.

# Impact

Any extension which relies on that attribute to configure themselves does not work for F#. One such extension is Durable Functions, which uses that attribute to inject services and configure options.

# Workaround

In environments where source generation does not run, applications will need to manually configure extensions on startup:

``` CSharp
Host.CreateDefaultBuilder()
.ConfigureFunctionsWorkerDefaults(app =>
{
new ServiceBusExtensionStartup().Configure(app);
});
```

Read sdk/Sdk.Generators/ExtensionStartupRunnerGenerator.cs and inspect WorkerExtensionStartupAttribute handling. Compare the generated startup path with the documented ConfigureFunctionsWorkerDefaults workaround, then reproduce the issue in an F# worker. Done means attributed extensions are invoked automatically during F# worker startup.

Written by the indexing model from the issue text.